1. Field of the Invention
The invention pertains to an autonomous kinematic measurement system for helicopters.
2. Description of the Prior Art
At present, helicopter navigation systems can be used to determine a helicopter's navigational parameters, such as its relative speed with respect to the ground (hereinafter designated as its ground speed), its direction angle .theta., defined as the angle between its longitudinal axis and the direction of the geographical North, and its relative speed with respect to the air (hereinafter designated as its airspeed), expressed according to its longitudinal component, Vax, parallel to the longitudinal axis xx of the helicopter, and its lateral component, Vay, parallel to an axis yy which is perpendicular to the longitudinal axis xx. For convenience, but non-restrictively, the longitudinal axis xx and the transversal axis yy of the helicopter intersect at the center of gravity G of the said helicopter and, when the helicopter is on the ground, they define a plane parallel to the said helicopter. Airspeed indicator units are used to determine the helicopter's airspeed. While these units give a very precise definition of the helicopter's airspeed, especially its longitudinal component, Vax, in the high speed range, namely for a longitudinal speed component, Vax, of greater than 50 knots or about 25 m/s, this is not so in the low speed range corresponding to speed components of less than 25 m/s and especially at the low hovering speeds of the helicopter. In this latter case, the the helicopter's airspeed can be obtained only by using special, expensive and delicate instruments which can hardly be considered for use except in the context of in-flight tests.
Present-day navigation systems for operational helicopters therefore lack constancy of precision in the measurement of airspeeds at low speed levels in the above-mentioned speed range. Furthermore, to remove this disadvantage, they depend on ancillary measuring instruments which are delicate and difficult to use.